Force analysis of the hand requires the development of a normative model for the internal tendon and joint forces which the finger and thumb joints resist during isometric pinch and grasp, verification of that model by in vitro and in vivo force testing, and application of the model to study pathologic conditions which affect the hand. Three studies are planned to complete the analysis of finger and thumb forces and to apply the results to the development of joint reconstructive procedures including joint prosthetic replacement. (1) The flexor tendon complex, including the retaining flexor pulley system, will be studied: (a) by incorporating a muscle length-tension relationship into the finger force model, the changes in muscle-tendon length will be reflected in pathologic force analyses; (b) by measuring the tendon forces at the tendon pulley interface, the applicants will examine the effects of sheath and pulley injury or disease that directly affect tendon moment arms and joint reactive forces. The longitudinal friction resistances between the tendon and tendon sheath along the entire pulley system will also be measured. (2) The extensor tendon forces will be studied in order to determine their contributions to the balance of joint forces. Three-dimensional geometric changes in the extensor tendon mechanism will be analyzed as a function of finger joint position and distributed force between the extrinsic and intrinsic muscles. Measurements of mechanical properties of the different segments of the extensor mechanism will also be performed. An analytic model based on a finite element analysis of the extensor mechanism will assist in resolving the extensor tendon force distribution. This will have application to the study of clinical problems of ulnar drift deformity, Swan neck deformity, and Boutonniere deformity. Proposals for rebalancing of pathologic forces through simulation may result. (3) Combining knowledge from previous studies on joint surface geometry, ligament alignment, joint center of rotation with the moment arm data of flexor and extensor tendons from the current proposal, prostheses to replace the thumb and finger joints will be studied. Techniques measuring tendon-excursion with respect to joint displacement will be used to comparatively assess moment arm changes and in turn predict the ability of different prostheses to duplicate normal finger and thumb joint motion.